A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.
1. Field of the Invention
This invention relates generally to computer systems, and more particularly provides a system and method for digitally marking a file with a removable mark.
2. Description of the Background Art
Real world data, such as audio and video data, are recorded on various mediums. Older technology, such as analog audio and video tapes, analog photographs, television and radio signals, etc., record real world data in analog form. Analog data on an analog medium is difficult to modify undetectably.
However, modern systems use digital technology. Examples of such systems include digital audio recordings on tape or CD""s or computer memory or hard disks, digital still or motion pictures on tape or DVD""s or in computer memory or hard disks, digital still or motion pictures or digital audio data sent over the phone lines or on computer networks, digital audio signals sent over the radio waves in devices such as digital microphones or cordless telephones. Because of the ease of data manipulation of a digital file, it is difficult to detect whether recorded digital data is the original real world data or a modified version.
Some prior digital imaging systems add a xe2x80x9cdigital watermarkxe2x80x9d to an image. A user typically selects a region in the image in which to replace the original real world data with a word or symbol. The digital watermark is designed to survive many types of digital editing and alteration. However, the digital watermark irrecoverably sacrifices some of the real world data and merely provides evidence of the origin of the digital work. Further, one hoping to authenticate the contents of the image cannot reasonably assume by locating the watermark in the image that the image contains only the original real world data.
Other prior digital systems append code to the real world data file containing the real world data. However, each system uses a different protocol and format. Thus, when converting a digital file between formats, the appended code is typically discarded as unnecessary. A user can thus modify the contents of the data file undetectably.
Further, compression is a technique used to reduce memory and processor power requisites. When an image is compressed using a form of lossy compression, the image content will be modified.
Therefore, a system and method are needed for encoding into a digital file a mark, which may not irrecoverably sacrifice any of the original data, which may not be lost by converting the file data between different protocols and formats, which may identify the original content, and/or which may survive lossy compression.
The present invention provides a system and method for marking any data file that contains a xe2x80x9cflatxe2x80x9d area, i.e., a set of data values wherein all the data values vary within a certain amount of each other. The flat area can be located within any pattern of values. The length of the set can be any number of data values greater than one (1). In a digital picture, examples of flat areas may include a set of navy blue pixels, a set of fire-engine red pixels, etc. In an audio recording, examples of flat areas may include a set of sound samples of a particular volume. Flat areas are almost always found in recordings or transmissions of natural information, e.g., a still picture, a motion picture, an audio recording, an audio transmission, a measurement of radio signals or other forms that occur in nature, etc. Examples of flat areas in real life may be found in data representing a sky, a tree, a speaker""s voice, a bass guitar solo, etc.
An example system and method place a content-identifying mark within the flat area of the data file. If alteration is performed on the original data, either the mark will not match the data or the mark itself may be damaged. The system and method attempt to modify the original data as little as possible, enable removal of the mark from the data, and, if unmodified, enable return of the original data. This would help ensure the integrity of the digital data involved and has many applications including ensuring the validity of digital photographs, digital motion pictures and digital voice or sound recordings for use as evidence in a court of law. Another use ensures the validity of scientific research data recorded by instruments or the validity of data transmitted over computer networks, radio transmission or other means. Other example systems and methods can place a copyright notice, an author""s name, an identification number, an authenticator""s number, the camera manufacturer""s number, digital data licensee""s information, etc. in the captured frame.
The system comprises an encoder and a decoder. The encoder includes a target area locator for locating in digital data a predetermined pattern of values that represents a flat area, and a marker for modifying values in the flat area to encode a mark into the flat area. The decoder attempts to extract the mark from the digital data. The decoder includes a mark area locator for locating a predetermined pattern of values in digital data, and an unmarker coupled to the mark area locator for examining the values to determine the state of each value and extract an embedded mark from the predetermined pattern of values.
The method comprises an encoding method and a decoding method. The encoding method encodes a mark into digital data, and includes locating in digital data a predetermined pattern of values that represents a flat area, and modifying values in the flat area to encode a mark into the flat area. The decoding method attempts to extract a mark from digital data, and includes locating a predetermined pattern of values in digital data, and examining the values to determine the state of each value and extract an embedded mark from the predetermined pattern of values.
The system and method may advantageously detect altered data to a configurable level of confidence. The system and method may advantageously allow the original digital data to be completely restored to it""s unmarked original state. The system and method may mark the digital data in a subtle way, so that the mark is not easily noticed if displayed in it""s marked state. The system and method may advantageously require no special preparation of the data. The system and method advantageously may be used with various types of digital data. The system and method advantageously require no human intervention. The system and method may advantageously provide a method of embedding information to survive lossy compression.